docs: def _is_permitted(self, identifiers, permission_s):
          """
          :type identifiers:  subject_abcs.IdentifierCollection
  
          :param permission_s: a collection of 1..N permissions
          :type permission_s: List of permission string(s)
          """
  
          for realm in self.realms:
              # the realm's is_permitted returns a generator
              yield from realm.is_permitted(identifiers, permission_s)